Here \({\bf k} = (k_x , k_y )\)  is the wave vector measured from the center of valley \(K_{\xi }\)  with valley index \(\xi = \pm 1\) , and \(k_{\mathrm {c}} = \gamma _1 / (\hbar v)\) . Block \(D\)  describes intralayer nearest-neighbor hopping with velocity \(v = (\sqrt{3}/2)a\gamma _0/\hbar \)  and in-plane lattice constant \(a\) , block \(V\)  describes interlayer hopping with parameter \(\gamma _1\)  between successive \(B_n\)  and \(A_{n+1}\)  sites.
For numerical diagonalization of (REF ) we use \(\gamma _0 = 3.16\,\) eV, \(\gamma _1 = 0.381\,\) eV [1]}, and \(a = 2.46\) Å.
